1. Field of the Invention
The present invention relates to a reflow soldering apparatus using circulated heated gas to solder electronic components to a circuit board while transporting the circuit board mounted with electronic components on a conveyor through a heating chamber.
2. Description of the Related Art
A reflow soldering apparatus is a device for heating a circuit board mounted with electronic components, melting the soldering paste and soldering the electronic components to the circuit board while the circuit board mounted with electronic components is transported by conveyor chain within a heated chamber.
A fan and a heater are installed in the reflow soldering apparatus to perform reflow soldering of the electronic components by heated gas. A reflow soldering apparatus of this type generally has a plurality of preheating chambers and one reflow soldering chamber arrayed along the transport direction of the conveyor chain. Each preheating chamber and reflow soldering chamber is installed with a fan and a heater. The fan and the heater are arranged above and below the conveyor chain. The gas heated by the heater is guided by a blow guidance means formed inside each chamber and blown onto the printed circuit board mounted with electronic components placed on the conveyor chain. The blow guidance means has a nozzle plate arranged horizontally and spaced apart from the printed circuit board on the conveyor chain. Heated gas from a plurality of nozzle holes formed in the nozzle plate is blown onto the printed circuit board mounted with electronic components.
The heated gas blown onto the edge section of the printed circuit board through the nozzle holes in the nozzle plate, heats the edge section of the printed circuit board and then flows to open spaces on the sides, so that gas heated to a specific temperature is constantly blown onto the edge section of the printed circuit board. However, after the heated gas blown onto the center section of the printed circuit board through the nozzle holes in the nozzle plate, heats the center section of the printed circuit board, this heated gas is not prone to flow to the open spaces on the sides, and tends to remain in that vicinity. As a result, a temperature difference occurs between the edge section of the printed circuit board and the center section of the printed circuit board, causing the problem of uneven distribution of heating temperatures.
In view of the above problems with the related art, the present invention has the object of providing a reflow soldering apparatus to render a smooth flow of heated gas so that the distribution of heating temperatures on the circuit board mounted with electronic components can be uniform.
To resolve the above mentioned problem with the related art, the present invention employs the following means. Namely, a reflow soldering apparatus using circulated heated gas to solder electronic components to a circuit board while transporting the circuit board mounted with electronic components on a conveyor through a heating chamber, comprises a plurality of gas passages formed at intervals along the transport direction of the conveyor, said gas passage having an opening for inflow of heated gas on the side facing the circuit board, and a first passage for the flow of heated gas into a blowing means from an opening different from the opening for inflow and formed in an intermediate portion of the gas passage.
The heated gas blown onto the circuit board mounted with electronic components, flows into the gas passage from the opening facing the circuit board side, and flows smoothly into the blowing means from the opening formed in the intermediate portion of the gas passage.
The present invention preferably has a second passage besides the first passage. In other words, the present invention preferably has a second passage for the flow of heated gas into the blowing means from an opening formed in an end portion of the gas passage.
In the present invention, after the heated gas blown onto the circuit board mounted with electronic components, flows into the gas passage from the opening facing the circuit board, besides flowing into the blowing means by way of the first passage, the heated gas also flows into the blowing means from the opening formed in the end portion of the gas passage, so that the heated gas is thus smoothly circulated.
The gas passage is for instance formed as a long, narrow passage intersecting the conveyor transport direction. The gas passage for blowing heated gas onto the circuit board is preferably provided between gas passages for inflow of heated gas and more preferably is formed between each of the gas passages for inflow of heated gas. In such cases, the gas passage for blowing heated gas onto the circuit board is for instance formed as a long, narrow passage transverse to the conveyor transport direction.
When the first passage and the second passage are provided, a structure in which the blowing means has intake openings on both opposite sides, and the heated gas flowing through the first passage is drawn into one of the intake openings, and the heated gas flowing through the second passage is drawn into the other intake opening, can provide smooth circulation of heated gas.
In that case, preferably a structure is provided where the blowing means has intake openings on the circuit board side and on the opposite side, and the heated gas flowing through the first passage from the opening formed in the intermediate portion of the gas passage is drawn into the intake opening provided on the circuit board side of the blowing means, and the heated gas passing through the second passage from the opening formed in the end portion of the gas passage is drawn into the intake opening provided on the opposite side from the circuit board.
The blowing means having intake openings in both opposite sides, besides being constituted by one fan or blower, may also be constituted by combining two fans or two blowers.
The blowing means preferably has intake openings on two sides as described above, but may also have an intake opening on one side.
In that case, when the first passage is present, a structure is preferably provided where the blowing means has an intake opening on the circuit board side, and the heated gas flowing through the first passage from the opening formed in the intermediate portion of the gas passage is drawn into the intake opening of the blowing means.
Further, when the first passage and the second passage are present, a structure is preferably provided where the blowing means has an intake opening on the circuit board side, and the heated gas flowing through the first passage from the opening formed in the intermediate portion of the gas passage is drawn into the intake opening of the blowing means, and the heated gas passing through the second passage from the opening formed in the end portion of the gas passage is drawn into the intake opening of the blowing means.
A fan or a blower is employed as the blowing means. A turbofan or a multiblade fan is for instance employed for the fan. When the fan has intake openings in both sides, the turbofan is preferable since the thickness of the fan can be decreased.
Air or nitrogen gas and the like is employed as the gas, however, nitrogen gas is preferable since oxidation is prevented.